<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .hsl-ring {
      width: 150px;
      height: 150px;
      border-radius: 50%;
      background: conic-gradient(#f00,
          #ff0,
          #0f0,
          #0ff,
          #00f,
          #000,
          #f0f,
          #f00);
      /* background: linear-gradient(to right, #ff0000, #00ff00, #0000ff); */
    }
  </style>
</head>

<body>
  <div class="hsl-ring"></div>
</body>

</html>